Anaerobic phenol oxidation by Geobacter metallireducens using various electron acceptors

The oxidation of phenol by the dissimilatory metal-reducing bacterium Geobacter metallireducens was studied with various terminal electron acceptors (TEAs) including: nitrate, ferric citrate, hematite (α-Fe ₂O₃), pyrolusite (β-MnO₂), and birnessite (δ-MnO_1.8). G. metallireducens (2 × 10⁸ cells mL^-1) oxidized phenol (0.10 mM) as the sole electron donor with ferric citrate (25 mM) as the TEA in less than 3 days, but required over 30 days with nitrate (3 mM). Only 0.03 mM phenol was oxidized with hematite (2 g L ^-1) as the TEA after 45 days. The electron shuttling compound anthraquinone-2,6-disulfonate (AQDS; 25 μM) was added to hematite suspensions and slightly increased the 45-day extent of phenol oxidation. No phenol was oxidized with pyrolusite (2 g L^-1). Abiotic oxidation of phenol by birnessite (2 g L^-1) required testing at a lower concentration (0.2 g L^-1). Phenol was completely oxidized with birnessite as the TEA after 30 days, while ca. 15% of the phenol was oxidized in corresponding abiotic controls.